Application Context & REPL

GoNest supports non-HTTP application contexts for CLI tools, workers, cron jobs, and microservice-only applications. It also provides an interactive REPL for debugging.

ApplicationContext

ApplicationContext bootstraps the DI container and module tree without starting an HTTP server. Equivalent to NestJS NestFactory.createApplicationContext().

ctx, err := gonest.CreateApplicationContext(AppModule)
if err != nil {
    log.Fatal(err)
}
defer ctx.Close()

// Resolve any provider from the container
container := ctx.GetContainer()
svc, _ := gonest.Resolve[*EmailService](container)
svc.SendBatchEmails()

Use Cases

CLI tools — resolve services and run commands without HTTP overhead
Workers — background job processors that share the same module/DI setup
Cron jobs — scheduled tasks that use application services
Testing — compile and inspect the module graph without a running server
Migrations — database migration scripts with access to the DI container

API

Method	Description
`CreateApplicationContext(module, opts...)`	Bootstrap DI without HTTP
`ctx.GetContainer()`	Access the root DI container
`ctx.Resolve(type)`	Resolve a provider by `reflect.Type`
`ctx.GetDiscoveryService()`	Runtime provider/controller discovery
`ctx.GetGraphInspector()`	Dependency graph analysis
`ctx.Close()`	Run shutdown hooks and tear down

Example: CLI Tool

func main() {
    ctx, err := gonest.CreateApplicationContext(AppModule)
    if err != nil {
        log.Fatal(err)
    }
    defer ctx.Close()

    migrator, _ := gonest.Resolve[*MigrationService](ctx.GetContainer())

    switch os.Args[1] {
    case "migrate":
        migrator.Up()
    case "rollback":
        migrator.Down()
    case "seed":
        seeder, _ := gonest.Resolve[*SeederService](ctx.GetContainer())
        seeder.Run()
    }
}

MicroserviceApp

MicroserviceApp combines ApplicationContext with a microservice transport server. Equivalent to NestJS NestFactory.createMicroservice().

app, err := gonest.CreateMicroservice(AppModule, gonest.MicroserviceOptions{
    Server: tcpServer,
})
if err != nil {
    log.Fatal(err)
}

// Start with graceful shutdown
app.ListenWithGracefulShutdown()

API

Method	Description
`CreateMicroservice(module, opts)`	Bootstrap microservice app
`app.Listen()`	Start the transport server
`app.ListenWithGracefulShutdown()`	Start with OS signal handling
`app.GetServer()`	Access the underlying transport server
`app.Close()`	Stop server and run shutdown hooks

REPL

The interactive REPL (Read-Eval-Print Loop) lets you inspect a running application from the terminal. Equivalent to NestJS REPL.

Starting the REPL

// For HTTP applications
app := gonest.Create(AppModule)
app.Init()

repl := gonest.NewREPL(app)
repl.Start()

// For application contexts
ctx, _ := gonest.CreateApplicationContext(AppModule)

repl := gonest.NewREPLFromContext(ctx)
repl.Start()

Available Commands

Command	Description
`help`	Show available commands
`modules` / `ls`	List all modules with provider and controller counts
`providers`	List all registered provider types
`controllers`	List all controllers
`routes`	List all registered HTTP routes (HTTP apps only)
`resolve <Type>`	Resolve a provider by type name
`methods <Type>`	List methods on a provider type
`debug`	Show the dependency graph summary
`exit` / `quit`	Exit the REPL

Example Session

GoNest REPL -- type 'help' for available commands, 'exit' to quit
> modules
Modules (3):
  [0] providers=5 controllers=2 global=false
  [1] providers=2 controllers=0 global=true
  [2] providers=1 controllers=1 global=false
> providers
Providers (8):
  - *config.ConfigService
  - *main.CatsService
  - *main.UsersService
  - *gonest.DiscoveryService
  - *gonest.GraphInspector
> routes
Routes (6):
  GET /cats
  POST /cats
  GET /cats/:id
  GET /users
  POST /users
  GET /health
> resolve CatsService
Resolved *main.CatsService: *main.CatsService
> methods CatsService
Methods on *main.CatsService (4):
  - Create(main.CreateCatDto) (main.Cat)
  - FindAll() ([]main.Cat)
  - FindOne(int) (*main.Cat)
  - Delete(int) (bool)
> debug
Dependency edges (3):
  *main.CatsController -> *main.CatsService
  *main.UsersController -> *main.UsersService
  *main.UsersService -> *config.ConfigService
> exit
Bye!

Custom I/O

Override stdin/stdout for testing or remote access:

repl := gonest.NewREPL(app)
repl.SetIO(customReader, customWriter)
repl.Start()

See example/25-context for a complete working example.